Orthodontic Treatment of Impacted Teeth. Adrian Becker

of radiation that these would generate is of the same order as that emitted by the new CBCT machines.

The many studies that have been undertaken, for patients with an impacted tooth, to compare the advantages of using CBCT over plain 2D radiography have not provided the conclusive evidence that one would expect. It is clearly an indisputable fact that 3D imaging has, at least in theory, provided an infinite number of possible angles from which to view the tooth, as compared with a 2D radiological representation. So why was there no conclusive result? Could it be that the range and depth of CBCT post‐processing techniques that were performed were not as sophisticated as they should have been? Or perhaps only a minimum/standard orthodontic service was offered by the imaging technicians for the individuals comprising the patient samples. It is our opinion that the technicians in many of the radiological institutes in most of the Westernized countries we have visited or with whom we have had professional communication have not succeeded in mastering the complexities involved in the sophisticated interpretation of the CBCT imaging modality.

Fig. 4.21 Multi‐planar reconstruction view. Arrows indicate the invasive cervical root resorption lesion in the first molar mesial root.

The greatest advantage that the cone beam volumetric machine has over conventional CT machines is that its radiation dosage is only a fraction of that emitted by the medical machine. As shown in Table 4.1, the CBCT machine irradiates the patient at approximately 8–23% of the regular CT machine, when 8% is compared to small FOV and 23% compared to craniofacial (extra‐large) FOV.

      Table 4.1 is based on typical exposure protocols and is calculated from data collated from multiple published studies. The levels of standard 2D dental radiography, CT and CBCT patients’ median effective dose are compared and are shown as equivalent to daily background radiation. An average small FOV effective dose is 50 μSv, while that of a dental panoramic is about 20 μSv. A complete mouth series done with a round collimator ranges from 100 (CCD) to 200 (photostimulable phosphor plate, PSP) μSv.

What do these figures mean to the lay public? With our responsibility as dentists to convey information in a manner understandable to those seeking our treatment and in order to obtain informed consent, it is imperative to present the issue in its context, without blinding the patient with scientific data. Thus, it may be more pertinent to use the comparison that (a) the average person receives a dose of about 8 μSv per day or 2700 μSv per year from the environment [28]; and (b) flying from New York to Tokyo by the transpolar route exposes the passenger to ionizing (cosmic) X‐rays of approximately 150 μSv and from New York to Seattle approximately 60 μSv [29].CBCT represents state‐of‐the‐art technology, with direct relevance to the determination of macroscopic anatomy and accurate positional diagnosis of impacted teeth. The machinery is not beyond the financial means of most hospitals, radiology institutes, imaging centres, dental clinics and dental school radiology departments. Its advantages to the orthodontist and surgeon are manifest. Its level of emitted ionizing radiation is low and the cost to the patient affordable. It is a recommended procedure for many of the cases discussed within the context of this book.

Table 4.1 Typical effective dose from radiographic examination.

      Source: Reproduced by kind permission of Dr S.M. Mallya and Elsevier Publishers.

Examination	Median Effective Dose	Equivalent Background Exposurea
Intra‐oral b
Rectangular collimation
Posterior bite‐wings: PSP or F‐speed film	5 μSv	0.6 day
Full‐mouth: PSP or F‐speed film	40 μSv	5 days
Full‐mouth: CCD sensor (estimated)	20 μSv	2.5 days
Round collimation
Full‐mouth: D‐speed film	400 μSv	48 days
Full‐mouth: PSP or F‐speed film	200 μSv	24 days
Full‐mouth: CCD sensor (estimated)	100 μSv	12 days
Extra‐oral
Panoramicb	20 μSv	2.5 days
Cephalometricb	5 μSv	0.6 day
Chestc	100 μSv	12 days
Cone beam CTb
Small field of view (<6 cm)	50 μSv	6 days
Medium field of view (dentoalveolar, full arch)	100 μSv	12 days
Large field of view (craniofacial)	120 μSv	15 days
Multidetector CT
Maxillofacialb	650 μSv	2 months
Headc	2 mSv	8 months
Chestc	7 mSv	2 years
Abdomen and pelvis, with and without contrastc	20 mSv	7 years

      ^a Approximate equivalent background exposure is calculated based on an estimated background radiation dose of 3.1 mSv/year. Exposures more than the equivalent of 3 days are rounded off to the nearest day, month or year.

      ^b Median dose from dento‐maxillofacial radiography with typical exposure protocols is calculated from data collated from multiple published studies. Doses in the range of 10–1000 μSv are rounded off to the nearest multiple of 10.

      ^c American College of Radiology, https://www.acr.org/Clinical‐Resources/Radiology‐Safety/Radiation‐Safety.

      CCD, charge‐coupled device; CT, computed tomography; PSP, photostimulable phosphor.

      Having said that, however,